Apparatus for the precision metering of fluids

ABSTRACT

There is disclosed a first capillary conduit having a minute aperture therein, the aperture dividing the first conduit into a separate and a common section, there being a first fluid conducting path formed through the separate and common sections. A second capillary conduit has one end thereof intersecting the first conduit and mating with the minute aperture to form a second fluid conducting path through the second conduit and the common section of the first conduit. The minute aperture forms a first precise interface between the first fluid path and the second conduit. The capillary cross-section of the first conduit separate section adjacent the minute aperture forms a second precise interface between the second fluid conducting path and the separate section, whereby fluid can traverse the first fluid path substantially free from contamination from fluids adjacent the first precise interface and fluids can traverse the second path substantially free from contamination from fluid adjacent the second precise interface.

United States Patent 1191 1 Liston Aug. 27, 1974 APPARATUS FOR THEPRECISION METERING OF FLUIDS [75] Inventor: Max D. Liston, NewportBeach,

Calif.

[73] Assignee: Abbott Laboratories, North Chicago, Ill.

[22] Filed: Dec. 22, 1972 21 Appl. No.: 317,753

Primary Exa'minerRobert G. Nilson Attorney, Agent, or Firm-Raymond L.Madsen ABSTRACT There is disclosed a first capillary conduit having aminute aperture therein, the aperture dividing the first conduit into aseparate and a common section, there being a first fluid conducting pathformed through the separate and common sections. A second capillaryconduit has one end thereof intersecting the first conduit and matingwith the minute aperture to form a second fluid conducting path throughthe second conduit and the common section of the first conduit. Theminute aperture forms a first precise interface between the first fluidpath and the second conduit. The capillary cross-section of the firstconduit separate section adjacent the minute aperture forms a secondprecise interface between the second fluid conducting path and theseparate section, whereby fluid can traverse the first fluid pathsubstantially free from contamination from fluids adjacent the firstprecise interface and fluids can traverse the second path substantiallyfree from contamination from fluid adjacent the second preciseinterface.

9 Claims, 8 Drawing; Figures 0/0/1214 arnm/va Mara/v ntcmaN/c FROGkAMcan/r004 com-n04 :ucma/wc ause/1M CONTROL ca/vmaL 1 il a/a/rm STEPP/A/GMara/7 The present invention relates to the precision aspiration anddispersion of fluid and more particularly to sample aspirating anddispensing systems for chemical analysis of blood serum.

In the field of chemical analysis of blood serum, it has been thegeneral practice to employ automated and semiautomated equipment toperform the desired chemical and analytical tests upon blood serum.These automated systems duplicateactual test tube procedures. Each testis treated as a discrete entity and must be free fromcross-contamination or carry-over between the various chemical testsperformed. In these automated systems, samples generally are placed insmall cups that are positioned on a movable sample table. In order toperform the desired test, a predetermined quantity of sample must bedispensed into an individual reaction tube. These reaction tubes areadvanced by a conveyor system through a series of reaction stationswhere reagents are added, as required, and reactions proceed underprecise temperature control. The contents of each reaction tube aresequentially scanned colorimetrically to provide a measurement ofconcentration or reaction activity. An essential and critical part ofthe automated blood chemistry system is the serum aspirating anddispensing apparatus. This apparatus aspirates the serum sample from thesample cup and dispenses it into the reaction tubes. These functionshave been accomplished by a hydraulic system which gives a high degreeof precision and accuracy. Initially, a serum arm moves over the sampletable and an aspiration-dispensing needle travels to a pick-up position.It has been the practice to introduce an airinterface between thehydraulic fluid which is generally de-ionized water and the serumaspirated into the apparatus. The air interface prevents any mixingbetween the de-ionized water and the serum. In one prior art system,after the required amount of sample is aspirated, a delivery is madeback into the sample cup to assure that all test deliveries. will becorrect. The arm then moves over the reaction tube and programmed.deliveries of predetermined amounts of serum are deposited into eachindividual reaction tube. When sample dispensing into the reaction tubeis completed, the needie is washed and the system is flushed with thedeionized water. In a typical system, the amount of sample aspirated isabout 0.25 milliliters, or 250 lambda, plus a volume for each test to beperformed, which averages about 0.05 milliliters or 50 lambda.Therefore, the total sample volume required ranges from 0.3 millilitersfor one test and 1.05 milliliters for 16 tests. Although the serumsample aspirating and dispensing devices have served the purpose, theyhave not proved entirely satisfactory under all conditions of servicefor the reason that considerable difficulty has been experienced inprecisely controlling the aspirated and dispensed amounts of serum toaccuracies approaching V2 lambda. These problems have resulted from thevolume inaccuracies produced by the cushioning effect of the airinterface between the de-ionized water hydraulic fluid and the serum andin the formation of surface tension drops of serum at the end of theaspirating and dispensing needle, which can be of a size having a volumeof lambda.

Those concerned with the development of serum aspirating and dispensingsystems have long recognized the need for aspirating dispensingapparatus which accurately controls serum volumes approaching V2 lambdain precision and accuracy. The present invention fulfills this need.

One of the most critical problems confronting designers of apparatus forthe precision volume dispensing of blood serums has been the preventionof contamination and uncontrolled dilution of the serum. The presentinvention overcomes this problem.

The general purpose of this invention is to provide a precision fluidmetering device which embraces all the advantages of similarity employedfluid aspirators and dispensers and possesses none of the aforedescribeddisadvantages. To obtain this, the present invention contemplates aunique combination of a silicone oil hydraulic fluid and an intersectingcapillary conduit arrangement inthe fluid pick-up and dispensing needlewhereby inaccuracies of surface tension drops and fluid interface mixingare avoided.

An object of the present invention is the provision of the precisionaspiration and dispersion of fluid free from inaccuracies of surfacetension drops.

Another object is to provide precision hydraulic aspi ration anddispersion of fluids wherein the hydraulic fluid does not mix orcontaminate the fluids aspirated and dispersed.

A further object of the invention is the provision of a dual hydraulicfluid aspiration and dispersion system whereby a test fluid may beaspirated and dispersed by one hydraulic fluid which does not mix orcontaminate the test fluid and whereby the test fluid may be dispersedby the other hydraulic fluid to avoid inaccuracies of surface tensiondrops of the test fluid.

Still another object is to provide a first precise interface betweenfluid flowing in a first fluid path and fluid in a second fluid path anda second precise interface between fluid flowing in a second fluid pathand fluid in the first fluid path.

Another object of the present invention is the provision of two separatefluid paths having a common section with a first precise interfacebetween fluid traversing one fluid path and fluid in the other fluidpath and a second precise interface between fluid in the one fluid pathand fluid traversing the other fluid path.

Other objects and many of the intended advantages of this invention willbe readily appreciated as the same becomes better understood byreference to the following detailed description when considered inconnection with the accompanying drawing in which like referencenumerals designate like parts throughout the figures thereof andwherein:

FIG. 1 illustrates a partly mechanical and partly block diagram of apreferred system embodiment of the invention;

FIG. 2 illustrates a cross-sectional view of the fluid pick-up anddispensing needle probe of FIG. 1;

FIGS. 3(a), (b), (c), (d), and (.e) illustrate various fluid positionsin the pick-up and dispensing probe encountered during the operation ofthe fluid aspiration and dispersion system of FIG. 1; and

FIG. 4 illustrates a pictorial view of the pick-up probe embodiment ofthe invention.

Referring now to the drawings, there is shown in FIG. 1 (whichillustrates a preferred embodiment) a probe having common capillaryconduit sections 7 and separate capillary conduit section 9 whichtogether form a first capillary conduit and a first fluid path. A secondcapillary conduit 11 intersects the first capillary conduit at a minuteaperature therein to provide a second fluid path through common section7 and second capillary conduit 11. Fluid conduit 13 connects separatesection 9 of the first capillary conduit to diluent syringe 15. Fluidconduit 17 connects second capillary conduit 11 to silicone oil syringel9. Diluent syringe has fluid port or opening 21 in the side thereofconnected to diluent reservoir syringe 23. Piston 25 is located withindiluent syringe I5 and piston 27 is located within diluent reservoirsyringe 23. The interior volume of diluent reservoir syringe 23 isdesignated as volume 28. Shaft 29 connects piston 25 to bracket 31 whichin turn has a threaded opening therein into which screw 33 is engaged toform a screw-drive mechanism. Screw 33 in turn is connected to shaft 37of digital stepping motor by coupling 35. Digital motor 39 is connectedto electrical control 41 which in turn is connected to program control43. Electrical control 41 may be a typical electrical circuit used todrive digital stepping motors, which circuit is well known to thoseskilled in the application and control of stepping motors. Electricalcontrol 41 may also have an input circuit which can convert a digitalinput code to a corresponding electrical signal to drive the steppingmotor through a predetermined angular excursion. Circuits of this natureare well known and widely used to control the angular position of adigital stepping motor. Program control 43 may be a series of thumbwheelswitches which may be rotated to produce a desired digital code to theinput circuit of electrical control 41.

Silicone oil syringe 19 has fluid port or opening 45 in the side thereofconnected to silicone oil reservoir sy.--

ringe 47. Piston 49 is located within the interior volume of siliconeoil syringe l9 and piston 51 is located within the interior volume 52 ofsilicone oil reservoir syringe 47. Shaft 53 is connected to piston 49and to bracket 55, bracket 55 having a threaded opening therein whichengages screw 57 to form a screw-drive mechanism. Screw 57 is connectedto coupling 59 which in turn is connected to shaft 51 of digital motor.63. Digital motor 63 is connected to electrical control 65 which in turnis connected to program control 67. Electrical control 65 may beidentical to electrical control 41 and program control 67 identical toprogram control 43.

Turning now to FIG. 2, there is illustrated a crosssectional view of apreferred embodiment of the pickup and dispensing probe of theinvention. The first fluid capillary conduit path comprising commonsection 7 and separate section 9 is a short length ofa thin walledcapillary tubing having a minute aperture 8 located in the side thereofbetween common section 7 and separate section 9. Block 12, having secondcapillary conduit 11 drilled therein by drilling two intersecting rightangle capillary lumens, is soldered to the side of the first capillaryconduit path tubing so that one end of second capillary conduit path 11intersects and mates with minute aperture 8. Fluid conduit 13, which maybe a flexible plastic or teflon capillary lumen, is attached to the endof separate section 9 of the first fluid capil lary conduit tubing. Ashort section of capillary tubing 14 is soldered into the other end ofsecond capillary conduit path 11 in block 12. Fluid conduit 17, whichmay be a flexible plastic or teflon capillary lumen similar to conduit13 is fastened to capillary tubing l4.

FIGS. 3(a), (b), (c), (d), and (e) illustrate the fluid positions withinthe pick-up and dispersing probe during the different operatingconditions of the probe. In FIG. 3(a), the probe is shown in the fluidaspirating condition wherein fluid B, which may be a silicone oil, fillscommon section 7 and second fluid conduit path 11; and fluid A, whichmay be a saline solution fills separate section 9, forming an interfacewith fluid B at the end of separate section 9 adjacent to minuteaperture 8.

FIG. 3(1)) illustrates the fluids within the probe just after a testfluid C, which may be a blood serum, has been aspirated therein. Fluid Cfills common section 7 and second capillary conduit path 11 andcontinues on into fluid conduit 17 interfacing with fluid B therein.Fluid A in separate section 9 interfaces with Fluid C at the end ofseparate section 9 adjacent to minute aperture 8.

FIG. 3(0) illustrates the position of fluid within the probe after testfluid C has been flushed from common section 7 by forcing fluid Athrough common section 7 to the end thereof. Fluid A fills both commonsection 7 and separate section 9 and forms an interface with fluid C atminute aperture 8. Fluid C fills second capillary conduit path 11 andcontinues upward into fluid conduit 17 where it interfaces with fluid B.The amount of fluid C contained in second capillary conduit path 1 I andfluid conduit 17 depends upon the amount of test fluid C aspiratedtherein.

FIG. 3((1) illustrates the fluid position within the probe when aparticular aliquot of test fluid C has been dispersed from conduit 17and second conduit path 11 into common section 7. The volume size of thealiquot can be extremely small and may occupy all or a portion of commonsection 7, forcing fluid A therein out of the end of common section 7.In this manner, precision aliquots of one lambda or less may beobtained. The aliquot is dispersed from common section 7 by forcingfluid A from separate section 9 through commonsection 7 to the endthereof such that the fluids are in the position illustrated in FIG.3(c).

FIG. 3(a) illustrates the fluid positions within the probe when all'ofthe test fluid C has been dispersed from conduit 17 and second conduitpath 11 and the probe has been flushed out by dispersing fluid A fromseparate section 9 through common section 7 and out of the end thereof.

Turning now to FIG. 4, a pictorial view of a preferred embodiment of thepick-up and dispersing probe is illustrated. The first capillary conduitpath tubing comprising common section 7 and separate section 9 is shownsoldered to block 12 containing second capillary conduit path 11 (notshown) which is connected to short section of capillary tubing 14.

Operation of the invention can best be described first by reference toFIG. 1. Piston 25 of diluent syringe 15 is positioned to open port 21 toallow fluid from diluent reservoir syringe 23 to be forced from volume21 by piston 27 into the interior of diluent syringe l5. Piston 27 ismoved into volume 28 until the diluent fluid is expelled and dispersedout of common section 7 of the pick-up and dispersing probe, therebyfilling the interior volume of diluent syringe l5, fluid conduit 13 andseparate and common sections 9 and 7 of the pick-up and dispersingprobe. Piston 25 is then moved to close port 21, placing the diluentsyringe in-position for operation.

Similarly, piston 49 is moved to open port 45 in silicone oil syringe 19to permit fluid to be forced from volume 52 of silicone oil reservoirsyringe 47 by moving piston 51 into volume 52. Fluid from reservoirsyringe 47 is forced into the interior volume of syringe 19, fluidconduit 17, second capillary conduit path 11 and common section 7 of thepick-up and dispersing probe. Because of the small capillarycross-sections of the first capillary conduit tubing forming commonsection 7 and separate section 9, a very small interface is formedbetween diluent fluid A (FIG. 3) and silicone oil B (FIG. 3) therebyminimizing contamination and mixing. Further, the chemical and physicalproperties of silicone oil B further reduce the mixing with diluent Aand provide a substantially independent hydraulic fluid path within theprobe.

Piston 49 is then moved into the interior of silicone oil syringe 19closing port 45 and further dispersing the contents of silicone oilsyringe 19 into fluid conduit 17 through the probe and out of commonsection 7. This prepares silicone oil syringe 19 for the aspiration of atest fluid into the probe with the fluids in the position shown in FIG.3(a).

Program control 67, which may contain finger operated digital switches,programs electrical control 65 to produce a predetermined driving signalto digital motor 63 causing shaft 61 to rotate through a predeterminedangle which in turn rotates screw 57 to move bracket 55 and piston 49 ina direction to increase the interior volume of silicone oil syringe 19and aspirate test fluid C into the probe as illustrated in FIG. 3(1)).The use of silicone oil provides a non-mixing interface between testfluid C and silicone oil B. Furthermore, the small cross-sectional areaof the capillary tubing provides a precise interface between diluentfluid A and test fluid C at the end of separate section 9 adjacent tominute aperture 8. Since silicone oil syringe 19 may be a precision borecalibrated syringe, program control 67 can be operated to produce aprecise volume change of silicone oil syringe 19 to aspirate a precisevolume of test fluid C into the probe and into fluid conduit 17.

Before test fluid C is dispersed from the probe, fluid A may be forcedinto common section 7 of the probe as illustrated in FIG. 3(c) to removeand flush test fluid C therefrom thereby removing any surface tensiondrops at the end of the probe and enabling the dispersing of precisionaliquots of test fluid approaching one lambda. This is done by movingpiston 25 a fixed amount by operation of program control 43 to programelectrical control 41 to produce a drive signal to digital motor 39 toturn shaft 37 through a predetermined angle thereby turning screw 33 tomove bracket 31 and piston 25 a given amount into the internal volume ofdiluent syringe equivalent to the volume of common section 7. The amountof diluent fluid A used to perform this dispersion need be no more thanthe volume of the capillary common section 7.

To disperse test fluid C, the thumb-wheel switches of program control 67may be operated to program electrical control 65 to produce a drivesignal to digital motor 63 to turn shaft 61 and screw 57 through apredetermined angle to move bracket 55 and piston 49 a precise amountcorresponding to the precision volume of test fluid to be dispersed.Turning to FIG. 3(11). dispersion of test fluid C into common section 7forces an equivalent amount of diluent fluid A contained in commonsection '7 out of the probe in front of the precision volume of testfluid C dispersed therein. Therefore, a very small and precise aliquotof test fluid C is forced in common section 7 which can be a fractionalpart of the volume of common section 7. It should be clear that volumesof test fluid C larger than common section 7 can be dispersed with equalprecision. To complete the test fluid dispersion operation, piston 25 ofdiluent syringe 15 may be further moved a predetermined fixed amout torinse the aliquot of test fluid C contained in common section 7 from theprobe again placing the fluids in the position of FIG. 3(a). It shouldbe noted that the amount of diluent in every dispersing action added tothe test aliquot is always precisely the same and is equivalent to thevolume of common section 7. Therefore, comparative tests can be made onsuccessive test aliquots without inaccuracies caused by effects ofvarying dilutions.

After the last of test fluid C has been dispersed into common section 7,the section is flushed by forcing fluid A therethrough whereby thefluids take the position illustrated in FIG. 3(e). Here diluent fluid Anow occupies separate section 9 and common section 7 and interfaces withsilicone oil B at minute aperture 8. The probe is then flushed withsilicone oil from second conduit path 11 to take the fluid posit-ionillustrated in FIG. 3(a) where the probe is ready once more foraspiration of test fluid C.

It should be clear at this point that the invention provides a precisionaspirating and dispersing probe that eliminates the inaccuracies ofaspiration and dispersion of fluids caused by the formation of surfacetension droplets at the end of the probe. This makes it possible toobtain accuracies in fluid dispersion and aspiration heretoforeunobtainable. Furthermore, the use of silicone oil as a non-mixing,non-contaminating hydraulic fluid to interface with the test fluidswhich are being as pirated and dispersed provides an unique advancementin achieving further precision and accuracy heretofore unobtainable insystems using air interface and other types of hydraulic fluids.

The present invention finds particular use in the field of blood serumanalysis where precision aliquots of one lambda or less are desired andwhere dispersing into a multilicity of containers from one samplecontainer is required. Test fluids which are blood sera may be preciselyaspirated and dispersed to enable a larger number of chemical tests froma given volume of serum than heretofore possible. Since more chemicaltests can be performed on a given blood sample, the amount of bloodtaken from a patient for a given set of tests is minimized. The smallertest volumes also enable more rapid testing since less time is requiredfor aspirating and dispersing serum test aliquots.

It now should be apparent that the present invention provides a probearrangement and an inert hydraulic fluid which may be employed inconjunction with a precision fluid metering system for the precise andaccurate aspiration and dispersion of blood sera for chemical testingwithout the unwanted contamination and sample volume errors associatedwith the sampling systems used heretofore and with sample aliquots ofsmaller precision volumes than achieved heretofore.

Although particular components, etc., have been discussed in connectionwith a specific embodiment of a precision fluid metering probe andcontrol systems constructed in accordance with the teachings of thepresent invention, others may be utilized. Furthermore,

it will be understood that although an exemplary embodiment of thepresent invention has been disclosed and discussed, other applicationsand circuit arrangements are possible in that the embodiment disclosedmay be subjected to various changes, modifications and substitutionswithout necessarily departing from the spirit of the inveniton.

What is claimed is:

1. Apparatus for the precision metering of fluids,

comprising:

a first capillary conduit having a minute aperture therein, saidaperture dividing said first conduit into a separate and common section,said first conduit forming a first fluid conducting path through saidseparate and common section;

a second capillary conduit having one end thereof intersecting saidfirst conduit and mating with said minute aperture to form a secondfluid conducting path through said second conduit and said commonsection of said first conduit, said minute aperture forming a firstprecise interface between said first fluid path and said second conduit,and the capillary cross section of said first conduits separate sectionadjacent said minute aperture forming a second precise interface betweensaid second fluid conducting path and said separate section wherebyfluid can traverse said first path substantially free from contaminationfrom fluids adjacent said first precise interface and fluids cantraverse said second path substantially free from contamination fromfluids adjacent said second precise interface;

a first syringe connected to the end of said first conduit separatesection, said first syringe having a movable piston to change the volumethereof whereby fluids can be aspirated and dispersed through said firstfluid path;

a second syringe connected to the end of said second conduit, saidsecond syringe having a movable piston to change the volume thereofwhereby fluids can be aspirated and dispersed through said second fluidpath;

a first fluid contained within said first syringe and within said firstconduit separate section up to said second precise interface wherebydecreasing the volume of said first syringe by a precise amount forcessaid first fluid past said second precise interface and into said firstconduit common section thereby displacing any fluid contained in saidcommon section; and

a second fluid contained in said second syringe and within said secondconduit and said common section whereby increasing the volume of saidsecond syringe aspirates through said common section and into saidsecond conduit a test fluid into which the end of said common section isimmersed, said test fluid in said common section being displacedtherefrom by said first fluid, and whereby decreasing said volume ofsaid second syringe in metered increments dispenses said test fluid inprecise amounts from said second conduit into said common sectionwherefrom said precise amounts may be displaced by said first fluid.

2. The apparatus as described in claim 1 wherein said second fluid is asilicone oil.

3. The apparatus as described in claim 2 wherein said first fluid is asaline solution and said test fluid is blood serum.

4. The apparatus as described in claim 3 further ineluding;

first coupling means connected to said piston of said first syringe; and

a first digital stepping motor connected to said first coupling meanswhereby said piston of said first syringe is moved to increase anddecrease the'volume of said first syringe.

5. The apparatus as described in claim 4 further including:

second coupling means connected to said piston of said second syringe;and

a second digital stepping motor connected to said second coupling meanswhereby said piston of said second syringe is moved to increase anddecrease the volume of said second syringe.

6. The apparatus as described in claim 5 whereby each of said first andsecond coupling means, respectively, is a screw drive mechanismcomprising:

a threaded shaft attached to and turned by said digital stepping motor;and

means having a threaded opening therein for engaging said threadedshaft, said means being attached to said piston of said syringe wherebysaid volume of said syringe is increased and decreased.

7. The apparatus as described in claim 6 further including:

a pair of electronic circuit means each being connected to one digitalmotor for driving said digital motor; and

a pair of control means each separately attached to one of said pair ofelectronic circuit means for generating a coded electronic signal tosaid one of each pair of circuit means whereby each of said digitalmotors is driven in steps related to said coded signal.

8. The apparatus as described in claim 7 further ineluding:

a reservoir syringe for containing a reserve of saline solution; and

a fluid port located in the side of said second syringe and connected tosaid reservoir syringe for receiving fluid from said reservoir syringe.

9. The apparatus as described in claim 8 further including:

a reservoir syringe for containing a reserve of silicone oil fluid; and

a fluid port located in the side of said first syringe and connected tosaid reservoir syringe for receiving

1. Apparatus for the precision metering of fluids, comprising: a firstcapillary conduit having a minute aperture therein, said aperturedividing said first conduit into a separate and common section, saidfirst conduit forming a first fluid conducting path through saidseparate and common section; a second capillary conduit having one endthereof intersecting said first conduit and mating with said minuteaperture to form a second fluid conducting path through said secondconduit and said common section of said first conduit, said minuteaperture forming a first precise interface between said first fluid pathand said second conduit, and the capillary cross section of said firstconduit''s separate section adjacent said minute aperture forming asecond precise interface between said second fluid conducting path andsaid separate section whereby fLuid can traverse said first pathsubstantially free from contamination from fluids adjacent said firstprecise interface and fluids can traverse said second path substantiallyfree from contamination from fluids adjacent said second preciseinterface; a first syringe connected to the end of said first conduitseparate section, said first syringe having a movable piston to changethe volume thereof whereby fluids can be aspirated and dispersed throughsaid first fluid path; a second syringe connected to the end of saidsecond conduit, said second syringe having a movable piston to changethe volume thereof whereby fluids can be aspirated and dispersed throughsaid second fluid path; a first fluid contained within said firstsyringe and within said first conduit separate section up to said secondprecise interface whereby decreasing the volume of said first syringe bya precise amount forces said first fluid past said second preciseinterface and into said first conduit common section thereby displacingany fluid contained in said common section; and a second fluid containedin said second syringe and within said second conduit and said commonsection whereby increasing the volume of said second syringe aspiratesthrough said common section and into said second conduit a test fluidinto which the end of said common section is immersed, said test fluidin said common section being displaced therefrom by said first fluid,and whereby decreasing said volume of said second syringe in meteredincrements dispenses said test fluid in precise amounts from said secondconduit into said common section wherefrom said precise amounts may bedisplaced by said first fluid.
 2. The apparatus as described in claim 1wherein said second fluid is a silicone oil.
 3. The apparatus asdescribed in claim 2 wherein said first fluid is a saline solution andsaid test fluid is blood serum.
 4. The apparatus as described in claim 3further including; first coupling means connected to said piston of saidfirst syringe; and a first digital stepping motor connected to saidfirst coupling means whereby said piston of said first syringe is movedto increase and decrease the volume of said first syringe.
 5. Theapparatus as described in claim 4 further including: second couplingmeans connected to said piston of said second syringe; and a seconddigital stepping motor connected to said second coupling means wherebysaid piston of said second syringe is moved to increase and decrease thevolume of said second syringe.
 6. The apparatus as described in claim 5whereby each of said first and second coupling means, respectively, is ascrew drive mechanism comprising: a threaded shaft attached to andturned by said digital stepping motor; and means having a threadedopening therein for engaging said threaded shaft, said means beingattached to said piston of said syringe whereby said volume of saidsyringe is increased and decreased.
 7. The apparatus as described inclaim 6 further including: a pair of electronic circuit means each beingconnected to one digital motor for driving said digital motor; and apair of control means each separately attached to one of said pair ofelectronic circuit means for generating a coded electronic signal tosaid one of each pair of circuit means whereby each of said digitalmotors is driven in steps related to said coded signal.
 8. The apparatusas described in claim 7 further including: a reservoir syringe forcontaining a reserve of saline solution; and a fluid port located in theside of said second syringe and connected to said reservoir syringe forreceiving fluid from said reservoir syringe.
 9. The apparatus asdescribed in claim 8 further including: a reservoir syringe forcontaining a reserve of silicone oil fluid; and a fluid port located inthe side of said first syringe and connected to said reservoir syringefor receiving fluid from said reservoir syringe.